The present invention relates to a pulverizing mill and a reduction gear used therefor, and particularly to a coal pulverizing mill and a reduction gear used therefor.
In order to pulverize coal so as to be used for a thermal power generation, a coal mill has been conventionally employed. In this coal mill, coal prior to a pulverization is supplied from a coal supplying port provided in an upper portion. Then, several pulverizing rollers provided in a middle portion pulverize the coal dropping down between the pulverizing roller and a pulverizing ring on which a groove of the roller is formed. A reduction gear which transmits power for rotating the pulverizing ring is arranged below the pulverizing ring. Then, a direction of rotation is converted from a direction of a horizontal axis into a direction of a vertical axis by this reduction gear. An electric motor serving as a driving apparatus is connected to an input side of the reduction gear.
Embodiments of the coal pulverizing mill are described in U.S. Pat. No. 4,972,099 and Japanese Patent Unexamined Publication No. 5-288335, and an example of the reduction gear used therefor is described in Japanese Patent Unexamined Publication No. 8-89828.
In recent years, the capacity of the coal mill for the thermal power plant is increased, and the size of the pulverizing ring is enlarged. In a typical structure thereof, a diameter of the pulverizing ring is increased to 3 m. As a result, an amount of the coal which can be pulverized is significantly increased and a diameter of the coal is significantly reduced in comparison with those in the conventional structure, however, power of the pulverizing ring is increased and load of the reduction gear for transmitting the power is increased. Further, concerning a power plant in which the coal mill is placed, a plurality of, for example, five or six coal mills are placed in one power plant in place that only one coal mill is placed there. In the power plant in which a wide space is required as mentioned above, it is not preferable to employ a cooling water for cooling lubricating oil which lubricates bearings and gears used for the reduction gear and the mill in view that it is necessary to secure a piping space and a freedom of mutual arrangement of the mills is reduced.
In this case, in U.S. Pat. No. 4,972,099 mentioned above, various problems in lubricating the coal mill are listed up and it is described that auxiliary lubricating means is provided for solving the problems. Then, by filtering the lubricating oil so as to remove a contaminant contained in the lubricating oil from the lubricating oil, bearings and gears used for a ball mill are prevented from being abraded. As a result, it is possible to prevent the lubricating oil from being deteriorated due to the mixed material into the lubricating oil and prevent the lubricating parts such as the reduction gear and the like from being abraded, however, the other lubricating means is provided in addition to the normal lubricating means, so that the apparatus becomes complex.
Further, Japanese Patent Unexamined Publication No. 5-288335 describes pulverizing the coal by the coal mill and providing a gear box in a lower portion of the mill main body, however, does not disclose lubricating each of the members in the mill. Further, Japanese Patent Unexamined Publication No. 8-89828 describes setting a thrust bearing of the reduction gear for the mill to a tilting pad bearing in order to reduce vibration and noise, and positioning a center of the spherical surface of the pads between the inside and the outside of the case to which a thrust force is applied. However, also in this publication, no sufficient consideration is taken into cooling the lubricating oil and the lubricating portion in order to intend to reduce a space of the bearing for the mill or simplify the bearing for the mill.
In this case, an embodiment in which an air cooling structure is employed for intending to simplify the reduction gear is described in Japanese Patent Unexamined Publication No. 4-4349, however, the reduction gear is a common reduction gear, and no consideration is given to conditions for using the reduction gear for the mill such as a high temperature, a lot of dusts, heavy shock load of each of the gears in the reduction gear, and the like.
An object of the present invention is to provide a reduction gear for a coal mill which has a high reliability even in a condition that an environment around the coal mill is not good and which is provided with a simple cooling mechanism. Another object of the present invention is to provide a reduction gear for a coal mill in which a maintenance period is made long so as to improve an operability.
In order to achieve the objects mentioned above, in accordance with a first aspect of the present invention, there is provided a coal mill having several pulverizing rollers and a pulverizing ring on which a groove is formed, thereby pulverizing coal introduced between the pulverizing rollers and the pulverizing rings, comprising a reduction gear for a mill which transmits power for rotating the pulverizing rings from a motor to the pulverizing rings, a cooling fan which is provided in an input shaft of the reduction gear for the mill connected to the motor, and a radiator for cooling a lubricating oil lubricating the reduction gear for the mill, the radiator being arranged in a downstream side of the cooling fan.
In preferable, the reduction gear for the mill has a radiator portion, an oil pump portion and a filter portion which are sectioned as blocks, and the blocks are connected to each other via a flexible pipe.
In order to achieve the object mentioned above, in accordance with a second aspect of the present invention, there is provided a reduction gear for a mill which is provided in a coal mill for pulverizing raw material coal introduced between a roller and a ring, comprising a cooling fan which is provided in an input shaft of the reduction gear for the mill connected to a motor, and a radiator for cooling a lubricating oil lubricating an inner portion of the reduction gear for the mill, the radiator being arranged between the cooling fan and a case of the reduction gear for the mill.
Further, it is desirable that the case of the reduction gear for the mill is extended to a side of the input shaft, the radiator is arranged in each of an upper portion and both side portions of the extending portion, and the radiators are connected in series by using a pipe, or the radiator is constituted by winding a pipe within which the lubricating oil is communicated around a periphery of the extending portion at several times.
Further, the structure may be made such that the radiator is sectioned as blocks, an oil pump portion and a filter portion which are sectioned as blocks are provided, and the blocks are connected to each other via a flexible pipe. Further, in preferable, each of the blocks is mounted to the case of the reduction gear via vibration isolating means.
Further, in preferable, a detachable filter cartridge is arranged between the radiator and the cooling fan, or a filter cartridge has an area which covers a front surface in a side of the cooling fan of the radiator.
Further, it is desirable that a first duct which covers a periphery of the cooling fan and a second duct which covers a periphery of the radiator are provided, and the first duct is formed in a shape which smoothly expands from an outer peripheral portion of the cooling fan to a front surface in a side of the cooling fan of the radiator, or the second duct is formed in a shape such that a cross-sectional area of air flow thereof gradually expands in a side of a back surface of the radiator (in an opposite side of a surface opposing to the cooling fan).